The present invention relates to a liquid core waveguide and particularly to a liquid core waveguide for fluorescence spectroscopy.
In earlier International Application PCT/US99/09395 (Publication No. WO 99/157584) entitled xe2x80x9cLiquid Core Waveguide,xe2x80x9d there is disclosed a new and useful liquid core optical waveguide which is particularly suitable for long pathlength absorbance spectroscopy. The waveguide is formed from flexible tubing having a flexibility and structural integrity allowing it to be coiled into a small volume without crimping. By this means, waveguides having long optical pathlengths can be provided in very compact spaces.
In accordance with the present invention, it has now been discovered that liquid core waveguides of the type described in the above-noted International Application PCT/US99/09395 and having long optical pathlengths in very compact spaces can also be made especially for use in emission spectroscopy such as fluorescence spectroscopy and the like.
In accordance with the present invention, a liquid core waveguide (LCW) comprises a flexible tube providing a liquid core and a light coupling for at least one end of the flexible tube. The flexible tube (i) has a substantially circular cross section and a substantially constant diameter, (ii) an index of refraction less than the index of refraction of a liquid which is disposed in the flexible tube, and (iii) is made from a material such that a cylindrical tube made from such material and having a liquid core diameter of about 560 xcexcm. an outer diameter of about 800 xcexcm and a length of about 5 meters can be coiled within a volume space of about 1.57 cubic inches and support a body of aqueous medium over its length without crimping.
A liquid core waveguide device for fluorescence spectroscopy, according to one preferred version of the present invention, includes a liquid core comprising a flexible tube which is configured into a coil, and is transmissive to light in relatively short wavelengths (e.g. ultraviolet light). The flexible tube has at least one light outlet (or xe2x80x9clight coupling devicexe2x80x9d) through which longer wavelength light (e.g. visible light) can pass. A light source is disposed at least partially within the coil and is configured to direct light of a relatively short wavelength range into the flexible tube to excite molecular material in the liquid core. The flexible tube is configured to contain a portion of light emissions of a longer wavelength (e.g. visible light) from the excited molecular material in the liquid core and to direct such portion of longer wavelength light emissions toward the light outlet.
According to one version of the present invention, the flexible tube has a plurality of light outlets, each configured to transmit longer wavelength light emissions. Moreover, the flexible tube is configured to direct the portion of the light emissions toward each of said plurality of light outlets, and a light coupler is provided in communication with each of the plurality of light outlets. The light coupler is configured to couple the light emissions from the plurality of light outlets and to direct the coupled light emissions from the plurality of light outlets to a spectrophotometric device for analyzing such light emissions.
In another preferred version of the present invention each of the plurality of light outlets has a coupling device with a graded index (GRIN) lens for providing a predetermined profile to the light emissions exiting from each respective light outlet. Moreover, the flexible tube has a liquid core with a substantially constant cross section circular inner diameter, the GRIN lens at each light outlet has a cylindrical profile with a circular cross sectional diameter which is greater than the circular cross sectional diameter of the flexible tube, and the GRIN lens at each light outlet is substantially coaxial with its respective light outlet. Thus, a substantial portion of the light emissions passing through such light outlet is captured by the GRIN lens associated with the light outlet.
Still further, according to another feature of the present invention, a substantially cylindrical support tube is provided, having a substantially constant outer diameter, and the flexible tube is wrapped in contiguous windings about the outer surface of the support tube to form a tight coil about the support tube. The light source is disposed at least partially within the support tube, and the support tube is configured of material that is transmissive of light in the relatively short wavelength range which is used to excite the molecular material in tile flexible tube. This feature enables the flexible tube to be wound tightly about the support tube without crimping (thereby to form the liquid core waveguide into a compact package), and enables light in the relatively short excitation wavelength range to be effectively) transmitted through the support tube and into the flexible tube.
In yet another aspect of the present invention, the light source is configured to allow selective control the wavelength of the ultraviolet light (or other light suitable to cause fluorescence) that is transmitted into the flexible tube. For example, the light source can comprise a light emitter (e.g. broadband or ultraviolet), and a light filter can be provided between the light emitter and the support tube, for controlling the wavelength range of light from the light emitter that is directed into the support tube. The light filter is moveable relative to the light source and the flexible tube, and includes a plurality of narrow band filters which enable selective control of the wavelength range of light within the excitation range which is transmitted from the light emitter to the flexible tube.
In still another aspect of the present invention, a liquid core waveguide capable of being used for both fluorescence spectroscopy and absorbance spectroscopy is provided. In this embodiment, flexible tubing transmissive to ultraviolet light is arranged about an ultraviolet light source in the same way as described above in connection with the other embodiments of the invention. However, in this embodiment, a tight source useful for absorbance spectroscopy (e.g. a source of visible light) is optically coupled to the connector at one end of the flexible tubing. When this device is used for fluorescence spectroscopy, it operates in much the same way as the other embodiments of this invention as described above in that light from the ultraviolet light source is transmitted into the flexible tubing and the fluorescence caused thereby is transmitted through the connector located at tile other end of the flexible tubing for detection by a spectrometer attached thereto. In this mode of operation, the source of visible light is inactive. However, when this device is used for absorbance spectroscopy, the operation of the lights is reversedxe2x80x94i.e., the visible light source is turned on while the ultraviolet light source is turned off. Accordingly, in this mode of operation, visible light is transmitted through the coupling on one end of the flexible tubing into the liquid core therein and attenuated light is transmitted through the coupling on the other end of the flexible tubing for detection by the spectrometer optically coupled thereto in a manner like that occurring with the wave guides shown in International Application PCT/US99/09395. In both modes of operation, measurements of high sensitivity can be obtained with a very compact system.
When operated in the fluorescence mode, the light source of the inventive wave guide is preferably an ultraviolet source, and the support tube is formed of quartz or another material which is substantially transmissive to light in the ultra violet range. Moreover, the flexible tube is preferably formed of Teflon(copyright) AF-2400 or other material that is substantially transmissive to light in the ultra violet range. Most preferably, the flexible tube is made from a material such as Teflon(copyright) AF-2400 which is substantially transmissive to ultra violet light and which also has an index of refraction less than that of water.
In an optional embodiment of the invention, the coupling devices through which liquid is directed into and out of the flexible tube, and through which light emissions are directed out of the flexible tube, are preferably formed with a graded index (GRIN) lens according to the principles described in commonly assigned U.S. Provisional Application Ser. No. 60/114,212, entitled Coupling Device For Liquid Core Waveguide, the disclosure of which is incorporated herein by reference. In this embodiment, each coupling device comprises a housing supporting a fluid connector, a light connector and a tube connector. Tile fluid connector is configured for attachment to a fluid conduit for directing liquid into or out of the tube. The light connector is configured for connection to a light conduit such as a light fiber for directing light to an analytical device such as a spectrometer. The tube connector is configured for connection to an end of the flexible tube, and a graded index (GRIN) lens is provided between the light connector and the tube connector to substantially focus light transmitted between the light connector and the flexible tube. The GRIN lens has a substantially cylindrical configuration, is supported in the coupling device in a co-axial relationship with the portion of the flexible tube disposed within the tube connector, and has a cross sectional area which is larger than the cross sectional area of the portion of the flexible tube disposed within tile tube connector, whereby the GRIN lens, when disposed to transmit light passing from the portion of flexible tube to a light conduit is oriented to capture substantially all of the light passing through the outlet of the flexible tube.
A liquid core waveguide device according to this form of the present invention is particularly configured for fluorescence spectroscopy, and comprises a flexible tube of the type described above, in a length of no more than 2 meters, coiled tightly about a quartz cylinder. An ultra violet light emitter is disposed within the cylinder, and is oriented to direct ultra violet light outward and through the cylinder and flexible tube, to excite molecular material within the flexible tube. In accordance with known fluorescence principles, the molecular material fluoresces, emits light in the visible range, and a substantial portion of that emitted visible light is retained in the flexible tube and directed by the flexible tube toward one or more light connectors, each of which is supported by a coupling device of the type described above. In each coupling device, substantially all of the emitted visible light is captured and focused by the GRIN lens, and directed to a light fiber (or fibers) which in turn transmit it to an analytical device.
A fluorescence based liquid core waveguide, which selectively controls the bandwidth of the ultraviolet light directly into the flexible tube, according to a specific aspect of the present invention, is intended to be particularly versatile, in the sense that it provides for selective examination and analysis of liquid samples under a number of selectively chosen light excitation sources and with a variety of materials in the liquid disposed in the flexible tube.
Further features of the present invention will become further apparent from the following detailed description and the accompanying drawings.